The present invention relates to an automatic transmission, and particularly relates to an automatic transmission that provides six forward speeds with plural planetary gear sets, clutches and brakes.
An automatic transmission that can provide a multi-speed shift by combining plural planetary gear sets, clutches and brakes is known.
Recently, an automatic transmission with six forward speeds has been demanded for improving a fuel economy or drivability.
Herein, gear trains of such an automatic transmission need to be properly compact because a layout space of the transmission is rather limited.
For example, U.S. Pat. No. 6,176,802 has proposed such a kind of automatic transmission, in which a reduction planetary gear and a Ravigneaux-type planetary gear set (a complex-type planetary gear set with a single common carrier), which inputs a reduction rotation and a non-reduction rotation and outputs plural rotation speeds, are provided coaxially, and speed-change elements of these planetary gears are connected or disconnected with three clutches and two brakes, thereby establishing the six forward speeds.
The above-described automatic transmission can prevent the size of rotational members from being improperly large and restrain a shift shock by reducing an inertia torque, in addition to its light weight and compactness, with its structure in which two clutches are respectively disposed on both sides of the Ravigneaux-type planetary gear set.
Although the above-described automatic transmission provides the light weight, compactness and small inertia torque, it has a problem in that since an increased drive torque is transmitted to the downstream clutches and the like because of a reduction function by the reduction planetary gear, a clutch capacity would be made large enough for this increased drive torque.
Further, the planetary gear set and other members that form the downstream gear trains may need a large torque capacity as well, so the size of the gear trains would become large inevitably.
Moreover, since this automatic transmission needs to use a long pinion that extends in an axial direction for the Ravigneaux-type planetary gear set, there is a problem in that the drive torque transmission with this long pinion would cause an improper inclination of gears which generates gear noises.